Range-change transmissions with a multi-step main transmission and a range group upstream or downstream from there, and with a splitter group upstream or downstream from the main transmission, have been known for a long time and are preferably used in utility vehicles. By virtue of, for example, a two-step splitter group with a transmission ratio interval that corresponds approximately to half of an average transmission ratio interval between two successive transmission ratio steps of the main transmission, the transmission ratio intervals of the main transmission are halved and the total number of available range-change gears is doubled. With a splitter group, for example with two steps, having a transmission ratio interval that corresponds approximately to half of an average transmission ratio interval between two successive transmission ratio steps of the main transmission, the transmission ratio intervals of the main transmission are halved and the total number of available range-change gears is doubled. And with a range group, for example with two-steps, having a transmission ratio interval above the overall transmission ratio interval of the main transmission by approximately an average transmission ratio interval between two successive transmission ratio steps of the main transmission, the transmission ratio range of the range-change transmission is approximately doubled and the total number of available gears is again doubled.
FIG. 1 shows a diagram of a range-change transmission of the so-termed AS-Tronic family produced by the present applicant. The range-change transmission CT shown in FIG. 1 comprises a main transmission HG, an upstream or splitter group GV in drive connection upstream from the main transmission HG and a range group GP connected downstream from the main transmission HG. The main transmission HG of the range-change transmission CT of FIG. 1 is configured as a direct-gear transmission of countershaft design and has a main shaft WH and two countershafts WVG1, and WVG2, the first countershaft WV1, being provided with a controllable transmission brake Br.
The main transmission HG is of three-step design with three transmission ratio steps G1, G2 and G3 for forward driving and one transmission ratio step R for reverse driving. Respective idler gearwheels of the transmission ratio steps G1, G2 and R are mounted to rotate on the main shaft WH and can be engaged by means of associated claw clutches. The associated fixed gearwheels are arranged in a rotationally fixed manner on the countershafts WVG1, WVG2.
The highest transmission ratio step G3 of the main transmission HG, made as a direct gear, can be engaged by means of a direct shifting clutch. The clutches of the transmission ratio steps G3 and G2 and the clutches of the transmission ratio steps G1 and R are in each case in the form of claw clutches and are combined in a common shifting packet, S1 or S2 respectively. The main transmission HG can be shifted without synchronization.
The upstream or splitter group GV of the range-change transmission CT in the sole FIG. 1 is of two-step configuration and also of countershaft design, such that the two transmission ratio steps K1 and K2 of the upstream group GV form two shiftable input constants of the main transmission HG. By virtue of a smaller transmission ratio difference between the two transmission ratio steps K1 and K2, the upstream group GV is designed as a splitter group. The idler gearwheel of the first transmission ratio step K1 is mounted to rotate on the input shaft WGE, which is connected via a controllable separator clutch K to a drive assembly (not shown) in the form of an internal combustion engine.
The idler gearwheel of the second transmission ratio step K2 is mounted to rotate on the main shaft WH. The fixed gearwheels of the two transmission ratios K1, K2 of the splitter group GV are respectively arranged in a rotationally fixed manner on extensions of the countershafts WVG1 and WVG2 on their input side. The clutches of the splitter group GV, which are synchronized and made as claw clutches, are combined in a common shifting packet SV.
The range group GP of the range-change transmission CT of FIG. 1, connected downstream from the main transmission HG, is also of two-step design but of planetary configuration with a single planetary gearset. The sun gear PS is connected in a rotationally fixed manner to the main shaft WH of the main transmission HG extended on its output side. The planetary carrier PT is coupled in a rotationally fixed manner to the output shaft WGA of the range-change transmission CT. The ring gear PH is connected to a shifting packet SP with two synchronized clutches made as claw clutches, by means of which the range group GP can optionally be shifted to a slow-driving step L by connecting the ring gear PH to a fixed part of the housing, or to a fast-driving step S by connecting the ring gear PH to the main shaft WH or to the sun gear PS. The range group GP can be shifted with synchronization.
From the countershaft WVG2 of the range-change transmission CT power can be branched off to drive an auxiliary PTO (Power Take-Off) drive. When power from the range-change transmission CT is to be branched off to drive the PTO auxiliary drive, then the procedure for engaging or switching on the PTO drive is such that first, by action upon the engine, an idling speed of the drive assembly is called for, the range-change transmission is then shifted into neutral and the separator clutch K is disengaged, and then the separator clutch K is engaged again so that when the separator clutch K has been completely engaged, the action upon the engine can stop.
Now, when the clutches of such a range-change transmission CT, made as claw clutches, are engaged, so-termed tooth-on-tooth positions can form in the claw clutches. However, tooth-on-tooth positions in shifting elements in the form of claw clutches impair the shifting comfort and result in increased wear of the shifting elements.
It is therefore important on the one hand to reduce the probability of tooth-on-tooth position occurrence, and on the other hand, should any tooth-against-tooth positions still occur, to release them safely, carefully and in a comfortable manner.
Although the invention is described in the context of a range-change transmission, its application is not intended to be limited to range-change transmissions, but rather, it can be used with transmissions of any type that comprise claw clutches.
From EP 1 895 201 A2 a method for operating a transmission is known, by virtue of which tooth-on-tooth positions in the transmission are released by applying a steady or pulsating braking torque to a transmission shaft by means of the transmission brake. Although with this method tooth-on-tooth positions can indeed be removed, the method is not able to reduce the probability of tooth-on-tooth positions occurring.